Published on the web September 28, 2011
1159
Synthesis and Characterization of Ni-doped Silica Membranes Prepared
Using a Hybrid SolGel/CVD Method
Sadao Araki,*1 Hiroyuki Yano, Shunsuke Tanaka, and Yoshikazu Miyake1,2
,2
1
1,2
1
Department of Chemical, Energy and Environmental Engineering,
Faculty of Environmental and Urban Engineering, Kansai University,
3
-3-35 Yamate-cho, Suita, Osaka 564-8680
2
High Technology Research Center, Kansai University, 3-3-35 Yamate-cho, Suita, Osaka 564-8680
(
Received July 1, 2011; CL-110553; E-mail: araki_sa@kansai-u.ac.jp)
Improving the hydrogen permeation flux, while maintaining
high hydrogen selectivity, is important for reducing membrane
areas and enhancing membrane reactor (MR) performance. We
have attempted to enhance the hydrogen permeation through the
addition of nickel, which will improve both hydrogen adsorption
and pore size control. The silica layer was deposited with high
selectivity, using an extended counter-diffusion CVD method.
dropwise to the mixture with gentle stirring at room temperature
3
,4
over a period of 15 min. The temperature was then increased
to 70 °C and the mixture was heated at reflux for 150 min. The
¹
1
resulting solution was diluted to 0.1 mol L in ethanol. The
membrane substrate was dipped into the nickelsilica solution
for 10 s. Finally, the membrane was dried at room temperature
for 3 h and calcined at 873 K for 3 h.
The silica was deposited using counter-diffusion CVD with
tetramethoxysilane, TMOS (Kishida Chemical), and oxygen for
5
Hydrogen is widely used in chemical and petroleum
industries and has been predicted to be a clean fuel for polymer
electrolyte fuel cells (PEFCs) in the future. More than the half
1 h. The temperature was raised to 873 K under an argon
atmosphere. After reaching 873 K, the TMOS was introduced
to the outside of the ¡-alumina tube, bearing a £-alumina
interlayer, under an argon carrier gas at a flow of 200 mL min .
Oxygen was then introduced to the inside of the ¡-alumina tube.
The pressure of the TMOS feed side was adjusted to 0.2 MPa
using a back-pressure regulator.
Gas permeation experiments were performed for a range of
temperatures at a differential pressure of 0.1 MPa, using nitrogen
as sweep gas. The measurement gas was fed inside the tubular
membrane, with a nitrogen feed-rate outside the membrane
offset to 20 mL min . The flow rates for the sweep gas and the
permeated gas were measured using bubble flow meters, and
the concentrations of the gases were determined using a gas
chromatograph equipped with a thermal conductivity detector
(GC-8A, Shimadzu, Japan). The permeance was then calculated
based on the flow rate and the concentration of the measurement
gas.
¹
1
the hydrogen worldwide is produced from the steam reforming
1
(
SR) of natural gas, whose main feedstock is methane. In this
reaction, by-product gases, such as carbon dioxide, carbon
monoxide, and methane, in addition to hydrogen, make up the
reforming gas. Therefore, much research has been focused on
separation technologies, such as membrane separation. Of the
primary membrane materials, silica has attracted much attention,
owing to its high heat stability and low production cost.
¹
1
Recently silica-based membranes, which have high hydro-
gen permeance and high selectivity, have been prepared using a
hybrid processing method that combines the solgel and CVD
2
methods. In this study, a Ni-doped silica membrane is prepared
using a hybrid method involving the solgel and high-pressure
CVD methods. Ni-doped silica layers were prepared on
¡-alumina support with a £-alumina interlayer, using the sol
gel method. We have attempted to enhance hydrogen permeation
through the addition of nickel, which is expected to improve the
hydrogen adsorption and pore size control. Silica membranes
with a high selectivity were subsequently prepared using
counter-diffusion CVD, under high-pressure conditions at the
membrane side, where tetramethylorthosilicate (TMOS) is
supplied.
An ¡-alumina tube (10 mm o.d., 6 mm i.d., 35 mm length,
Noritake Co., Ltd.) with a £-alumina layer was used as the
membrane substrate. The porous ¡-alumina tube (35 mm length)
was joined to a dense ¡-alumina tube (10 mm o.d., 6 mm i.d.,
The relationship between temperature and both the hydro-
gen permeance and hydrogen selectivity over methane for the
typical membranes is shown in Figure 1. Hydrogen permeance
increased with increasing Ni content. This result may be caused
by the affinity of nickel for hydrogen. Moreover, all membranes
have a high hydrogen permeance at 100 °C, with values over
6
-
7
10
1
1
05
04
6
5
4
3
2
1
0
250 mm length) and an ¡-alumina disk (12 mm diameter, 2 mm
103
thickness) with a glass sealant. The £-alumina interlayers were
¹1
prepared by dipping ¡-alumina tubes into a 0.6 mol L
boehmite (£-AlOOH) sol, containing 1.5 wt % poly(vinyl alco-
hol). The tube was dried at room temperature for 3 h and then
calcined at 600 °C for 3 h, at a heating and cooling rate of
102
Open: Permeance
Close: Selectivity
Ni/Si = 0.5
Ni/Si = 0.25
Ni/Si = 0
101
600
¹
1
1
°C min
Tetraethoxysilane (20 g, Wako) was added after all the
nickel(II) nitrate hexahydrate (Ni/Si mol ratio = 0.5, 0.25, and
) had dissolved in ethanol. 1 M HNO3 (7.5 mL) was added
.
4
00
500
Temperature / K
0
Figure 1. Effect of temperature on permeance and selectivity.
Chem. Lett. 2011, 40, 11591160
© 2011 The Chemical Society of Japan
Araki, Sadao
